1. Field of the Invention
This invention relates to an electronic component mounting base board, and more particularly to a structure of an electronic component mounting base board for preventing the occurrence of warping in the base board during the sealing with a resin after the mounting of the electronic component.
2. Description of Related Art
As the electronic component mounting base board, there was a base board formed by adhering and fixing a heat sink to a surface of an insulating substrate in the past. In this case, the positioning of the insulating substrate and the heat sink was carried out by using a positioning guide.
The inventors have already proposed an electronic component mounting base board of a structure capable of facilitating the positioning between the substrate and the heat sink (Japanese Patent Application No. 9-67408). That is, as shown in the comparative example of FIGS. 15 and 16, a projection portion 913 extending from a side face of a heat slug 91 is inserted into a positioning hole 96 formed in an insulating substrate 95 and joined and fixed to the substrate through a solder 94. Thus, the positioning between the heat slug 91 and the insulating substrate 95 is carried out by inserting the projection portion 913 into the positioning hole 96.
An insulating resin adhesive layer 92 is interposed between the heat slug 91 and the insulating substrate 95.
And also, a conductor circuit 93 is formed on the insulating substrate 95, while the surface of the insulating substrate 95 is covered with a solder resist 97.
In substantially a central portion of the insulating substrate 95 is formed a concave mount portion 951 for mounting an electronic component. As shown in FIG. 16, an electronic component 952 is adhered onto the mount portion 951 through an adhesive 953 and thereafter a sealing resin 954 is filled in the mount portion 951.
In the sealing of the mount portion 951 with the sealing resin 954, however, the sealing resin is filled into the mount portion 951 at a molten state and then cured. As a result, the sealing resin 954 shrinks as shown in FIG. 16, but the heat slug 91 does not shrink. For this end, a side of the insulating substrate 95 opposite to the heat slug 91 is shrunk by the shrinkage of the sealing resin 954 to cause warping of the insulating substrate 95. In case of causing such a warping, the connection reliability of the electronic component mounting base board to a surface mount device lowers.